Nitrogen uptake during one year in subarctic plant functional groups and in microbes after long-term warming and fertilization

TY - JOUR

T1 - Nitrogen uptake during one year in subarctic plant functional groups and in microbes after long-term warming and fertilization

AU - Sørensen, Pernille Lærkedal

AU - Michelsen, Anders

AU - Jonasson, Sven Evert

N1 - Paper id:: doi:10.1007/s10021-008-9204-6

PY - 2008

Y1 - 2008

N2 - For the first time in an arctic long-term warming and fertilization experiment, the short-term (days) and longer-term (month and year) nitrogen (N) uptake and allocation in plants, microbes, and soil pools were studied, with 15N-labeling of an organic nitrogen form, glycine. The long-term warming and fertilization had no marked effect on soil inorganic N content, but both dissolved organic N (DON) and plant biomass did increase after fertilization. Soil microbes initially immobilized most of the added 15N, but in the following months, they lost two-thirds, while label concentration in plants increased. After a year, however, the 15N recovered in microbes was still 10-fold higher than that in the plant biomass, showing the high importance of soil microbes in nutrient retention in arctic ecosystems, irrespective of the impact of long-term warming or fertilization. The effects of the treatments on the uptake of label by deciduous shrubs and evergreens paralleled that of their N pool sizes, suggesting that their N uptake potential was unaffected by long-term warming and fertilizer addition. Mosses and herbs had high uptake potential but in fertilized plots they took up less 15N, that is, they were N saturated. The fraction of 15N in microbes tended to decrease after fertilization, but this was an effect of higher N pool dilution after 1 month and a year, and not due to lower initial uptake. Although the concentration of soil inorganic N did not change after fertilization, both increased DON and the results of the 15N label addition showed that the N availability in the ecosystem had increased. By contrast, warming had little effect on soil N pools and microbial 15N uptake, and, hence, had no detectable effects on 15N accumulation.

AB - For the first time in an arctic long-term warming and fertilization experiment, the short-term (days) and longer-term (month and year) nitrogen (N) uptake and allocation in plants, microbes, and soil pools were studied, with 15N-labeling of an organic nitrogen form, glycine. The long-term warming and fertilization had no marked effect on soil inorganic N content, but both dissolved organic N (DON) and plant biomass did increase after fertilization. Soil microbes initially immobilized most of the added 15N, but in the following months, they lost two-thirds, while label concentration in plants increased. After a year, however, the 15N recovered in microbes was still 10-fold higher than that in the plant biomass, showing the high importance of soil microbes in nutrient retention in arctic ecosystems, irrespective of the impact of long-term warming or fertilization. The effects of the treatments on the uptake of label by deciduous shrubs and evergreens paralleled that of their N pool sizes, suggesting that their N uptake potential was unaffected by long-term warming and fertilizer addition. Mosses and herbs had high uptake potential but in fertilized plots they took up less 15N, that is, they were N saturated. The fraction of 15N in microbes tended to decrease after fertilization, but this was an effect of higher N pool dilution after 1 month and a year, and not due to lower initial uptake. Although the concentration of soil inorganic N did not change after fertilization, both increased DON and the results of the 15N label addition showed that the N availability in the ecosystem had increased. By contrast, warming had little effect on soil N pools and microbial 15N uptake, and, hence, had no detectable effects on 15N accumulation.

U2 - 10.1007/s10021-008-9204-6

DO - 10.1007/s10021-008-9204-6

M3 - Journal article

SN - 1432-9840

VL - 11

SP - 1223

EP - 1233

JO - Ecosystems

JF - Ecosystems

IS - 8

ER -